Going underground can slash energy usage say scientists

Scientists say that the US could cut its consumption of natural gas and electricity if it switched to the use of underground water to heat the country’s homes and businesses.

The study found that about 12% of the total global energy demand comes from heating and cooling properties but the use of underground water to maintain comfortable temperatures could reduce consumption of natural gas and electricity in this sector by 40% in the US alone.

The system called aquifer thermal energy storage (ATES), could also help prevent blackouts caused by high power demand during extreme weather events.

“We need storage to absorb the fluctuating energy from solar and wind, and most people are interested in batteries and other kinds of electrical storage. But we were wondering whether there’s any opportunity to use geothermal energy storage, because heating and cooling is such a predominant part of the energy demand for buildings,” said first author A.T.D Perera, a former postdoctoral researcher at Lawrence Berkeley National Laboratory (Berkeley Lab), now at Princeton University’s Andlinger Centre for Energy and Environment.

“We found that, with ATES, a huge amount of energy can be stored, and it can be stored for a long period of time,” Perera added. “As a result, the heating and cooling energy demand during extreme hot or cold periods can be met without adding an additional burden on the grid, making urban energy infrastructure more resilient.”

The study is one of the first examinations of how ATES could fit into the larger goal of decarbonising US energy systems by storing intermittent renewable energy to use when the sun isn’t shining and the turbines aren’t spinning. After building a comprehensive technological and economic simulation of an energy system, the authors found that ATES is a compelling option for heating and cooling energy storage that, alongside other technologies such as batteries, could help end our reliance on fossil fuel-derived backup power and enable a fully renewable grid.

The team said ATES is a “delightfully simple concept” that leverages the heat-absorbing property of water and the natural geological features of the planet. Water is pumped up from existing underground reservoirs and heat it at the surface in the summer with environmental heat or excess energy from solar, or any time of the year with wind. Then you pump it back down.

“It actually stays fairly hot because the Earth is a pretty good insulator,” explained co-author Peter Nico, deputy director of the Energy Geosciences Division at Berkeley Lab and lead of the Resilient Energy, Water and Infrastructure Domain. “So then when you pull it up in the winter, months later, that water’s way hotter than the ambient air and you can use it to heat your buildings. Or vice versa, you can pull up water and let it cool and then you can put it back down and store it until you need cooling during hot summer months. It’s a way of storing energy as temperature underground.”

ATES is not yet widely used in the US, though it is gaining recognition internationally, most notably in the Netherlands. One major benefit is that these systems get “free” thermal energy from seasonal temperature changes, which can be bolstered by the addition of artificial heating and cooling generated by electricity. As such, they perform very well in areas with large seasonal fluctuations, but have the potential to work anywhere, so long as there is wind or solar to attach to. In regard to other impacts, ATES systems are designed to avoid impinging upon critical drinking water resources – often the water used is from deeper aquifers than the drinking water supply – and do not introduce any chemicals into the water.

The results of tests ion the potential for its use in Chicago showed that adding ATES to the grid could reduce consumption of petroleum products by up to 40%, though it would cost 15 to 20% more than existing energy storage technologies.

“But, on the other hand, energy storage technologies are having sharp cost reductions, and after just a few years of developing ATES, we could easily break even. That’s why it’s quite important that we start to invest in this research and start building real-world prototype systems,” said Perera.

“ATES does not need space compared with above-ground tank-based water or ice storage systems. ATES is also more efficient and can scale up for large community cooling or heating compared with traditional geothermal heat pump systems that rely on heat transfer with the underground earth soil,” added Tianzhen Hong, a co-author and senior scientist at the Building Technology and Urban Systems Division.

The team said another major benefit of ATES is that it will become more efficient as weather becomes more extreme in the coming years due to climate change. The hotter summers and harsher winters predicted by the world’s leading climate models will have many downsides, but one upside is that they could supercharge the amount of free thermal energy that can be stored with ATES.

“It’s making lemonade, right? If you’re going to have these extreme heat events, you might as well store some of that heat for when you have the extreme cold event,” said Nico.

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